This invention relates to a pressure sensor, and more particularly to a capacitive pressure sensor which detects the deviation of a diaphragm responsive to a pressure in the form of a change in an electrostatic capacity.
As disclosed in, for example, U.S. Pat. No. 3,232,114, a capacitive pressure sensor has heretofore been provided in which a resilient diaphragm is formed of metal under uniform tension. It is required of the capacitive pressure sensor that the proportionality (linearity) between the input pressure and the output voltage is high. For meeting this requirement, it is a very important factor that the diaphragm is formed under uniform tension. In the disclosure of the above patent, the diaphragm is maintained under a stress of approximately 60,000 pounds, and its marginal portion is disposed between and is welded to two metal housing sections. The diaphragm, for the above reasons, must be carefully welded to the two housing sections while in stressed condition. Such a process has been carried out with, for example, arc welding or electron-beam welding. However, it has been very difficult to fix the diaphragm under the high tension and uniform state, resulting in the disadvantage of low productivity.
In U.S. Pat. No. 3,793,885, there is disclosed a diaphragm construction for a capacitive pressure transducer in which the measuring components, particularly a pressure-deformable diaphragm, are constructed from a brittle material, such as fused quartz, to take advantage of low hysteresis and creep factors and a low thermal coefficient of expansion. However, the brittle materials disclosed in this patent are insulators, and a conductor must be evaporated onto the surface of the pressure-deformable diaphragm formed of the insulator. In addition, the shape of the diaphragm is cylindrical.
Various techniques for joining elements are also known in the art; for example, U.S. Pat. No. 3,397,278 discloses an anodic bonding technique.